In the food packaging industry various techniques exist for sequentially exposing containers of food product to a vacuum or to an inert atmosphere to substantially reduce the oxygen level, and for sealing the container to retain the applied vacuum or atmosphere and thereby preserve freshness of the food products. Existing systems have limitations which reduce the efficiency and speed of the packaging operation. In addition, certain packaging system designs remove the choice of using a variety of modern filling and seaming equipment.
The problem becomes more acute when considering processes that require vacuum packaging. For example, the coffee industry requires vacuum packing to remove destructive oxygen thereby minimizing degradation of flavor volatiles and reducing the effect of the ground roasted coffee out-gassing for overall consumer acceptance. Within a twenty-four hour period after the coffee is ground and roasted a relatively high percentage of carbon dioxide within the coffee is gassed off. Existing coffee packaging systems generally provide a vacuum of between about 27-28 inches of mercury (wherein zero inches being atmospheric pressure and approximately 30 inches being a perfect vacuum) to the filled coffee containers to substantially remove the majority of destructive oxygen. This level of reduced pressure accommodates the gassing off and retains an adequate negative pressure to protect flavor volatiles within a permanently sealed container. If the container is exposed to an inadequate vacuum, a positive pressure may develop (depending on the product hold time after the coffee is ground and roasted) within the container as a result of the normal out-gassing which could project coffee out of the container upon opening. Inadequate vacuum also would expose the coffee to a higher oxygen level both reducing equivalent shelf life and flavor impact upon consuming. This is both undesirable and potentially hazardous to the consumer.
Existing coffee packing systems have cumbersome seamer operations within a vacuumized chamber. These systems are cumbersome and inefficient having complex seaming rolls, substantial vacuum pumps, and air locks with metal on metal sealing chambers which require frequent maintenance due to the excessive wear. In operation, the filled containers pass through a clincher which partially crimps a lid onto a container to ensure the lid is retained on the container as it processed. Next, the container with lid passes through a two-stage airlock, with an initial stage at a pressure of for example approximately 15 inches of mercury. The second stage communicates with the main vacuum chamber with a pressure of approximately 27-28 inches of mercury. The residence time required in the air lock effectively limits the line speed of the packaging process to approximately 100-150 containers per minute (depending on end vacuum levels). The extreme vacuum ramp up in the two stage airlock causes a high degree of turbulence within the seaming chamber which contributes to the formation of a coffee dust blanket which is extremely corrosive and destructive to the seaming rolls and mechanics of the equipment. The containers next are fed into the double seamer which is enclosed within the vacuum chamber. The location of the seamer within the chamber complicates the maintenance of the seamer and requires substantial energy expenditure to continuously evacuate the large seaming chambers. After seaming, the containers are released to atmosphere through another two stage air lock.
It would be desirable to have a sealing system that would accommodate both atmospheric pressure (e.g. inert gas) and vacuum packed products. A system providing a pre-seal prior to seaming would eliminate the need for the seaming equipment to reside within the inert gas environment or vacuum chamber. An incremental vacuumization processor, where vacuum sealing is desired, would allow the line speed of the system to be increased, such as to four times the existing line speeds by gradually pulling vacuum over many stages rather than abruptly pulling vacuum in two stage air locks. In addition, the incremental vacuumization and pre-seal operation followed by double seaming external of the vacuum chamber would eliminate the corrosive and destructive dust from damaging or wearing the high tolerance double seaming rolls and components. It would also be desirable to provide an inert gas environment in the input transportation system and filling system to reduce oxygen levels and accommodate less vacuumization. The lower vacuum levels would allow for light-weighting of the containers and lids.
Wet vacuumization processes used for packaging some vegetables, pasta and tomato sauce products, meat products, chili, soups, and other food products with moisture are also inefficient and cumbersome. These processes require filling open containers with the cooked food product at high temperature and exposing it to super-heated steam as it is transported to the seaming station. The steam exposure continues during the double seaming process. The steam effectively displaces the air in the container and, as the container cools, a vacuum is formed within the container. After the container is seamed, it is generally fed through a vertical or horizontal retort tank. The tank is filled with high temperature water and/or steam. The container remains in the tank for a minimum period of time sufficient to guarantee an effective kill of desired bacteria and other microbes. The exact period of residence time in the retort tank is determined by the thermal death curve which is product and container dependant. This time/temperature critical process is particularly important to kill pathogens, especially botulism which can cause illness or death if ingested. The retorting operation is a mandatory safety process and must be done to the full time/temperature minimum regardless of the prior cooking and steam exposure.
It would be desirable to have a system that would eliminate the need for filling with hot product and applying super-heated steam to the container during transportation and the seaming process. This would reduce energy costs and help improve the overcooked texture of many products which are recooked not only by the super-heated steam process, but again in the retort tank. An effective high speed system providing a pre-seal in a vacuumized environment would eliminate the need for steam purging during the double seam process. Inert gassing during transportation to the filler and pre-sealing stations, and inert gassing of the product in the filling station, would also eliminate the need for steam purging during transportation of the containers to the seamer.
One problem that arises in providing an effective pre-seal is the frequent imperfections that occur during shipment and handling of the containers. These imperfections include dents and indentions on the exposed flange and upper flange radius about the container opening. In addition, oblong or out of round container openings often result from shifting during shipping. These irregularities are acceptable in the canning industry because they are accommodated by the standard double seamers that operate to restore the container shape during seaming. In addition, the standard double seam lids have a curl portion which is folded into the flange thus avoiding the imperfections on the exposed flange and upper exposed flange radius.
These imperfections on the flange radius, however, would affect pre-sealing a standard double seam lid to the flange radius of the container. The various dents and indentations would provide a path between the mating surfaces of a draw portion of the standard lid and the flange radius and allow the vacuumized or inert environment to become contaminated when exposed to an atmospheric or other contaminating environment. It would accordingly be desirable to have a system that would provide a lid having a slightly deeper draw, if desired, with a slightly increased radius, that would allow the lid to seal against the lower flange radius and interior surface of the container to avoid the imperfections on the flange radius and provide an effective pre-seal. The increased draw radius would facilitate a plunger assisted insertion of the lid into a misshapen container opening during the pre-sealing process.